"In response to the hundreds of soldiers coming home from war with missing arms or legs, Darpa is spending millions of dollars to help scientists learn how people might one day regenerate their own limbs. Prosthetics are getting better all the time, but they will never be as good as the limbs we were born with. So two teams of scientists at 10 institutions across the country are competing to regrow the first mammalian limb ... The researchers' first milestone is to generate a blastema — a mass of cells able to develop into various organs or body parts — in a mammal."